In a wireless communication, failures in a wireless communication apparatus occur, such as a decrease in a received signal level (RSL), an increase in bit errors and an interception of communication, due to causes such as natural phenomena and instrument faults. It is necessary to identify a failure cause in order to cope with a failure of the wireless communication because a coping process differs according to the failure cause.
In relation to the above-mentioned technique, for example, Patent Literature 1 discloses a wireless apparatus identifies a failure cause in a wireless link between the wireless apparatus and another wireless station to execute a countermeasure. The wireless apparatus according to Patent Literature 1 acquires characteristic values of statistical information representing a state of the wireless link and detects a plurality of failure causes previously related to the statistical information, in a prescribed order based on the characteristic values. Further, the wireless apparatus according to Patent Literature 1 executes the countermeasure previously related to the detected failure cause. In Patent Literature 1, the plurality of failure causes include the existence of shadowing, the existence of radio wave noise, the existence of multipath fading, the existence of congestion and the existence of hidden terminals. The detection in the prescribed order means the following order: the detection of the existence of the shadowing, the detection of the existence of the radio wave noise, the detection of the existence of multipath fading, the detection of the existence of congestion, and finally the detection of the existence of hidden terminals.
Further, for example, Patent Literature 2 discloses a space diversity in-phase combining board (SD COMB board) used for a multiplex wireless apparatus in which the board detects whether an instrument abnormality or a line abnormality has occurred and transmits a notification. The SD COMB board includes first and second signal distributors that distribute (i.e., divide) input signal into two signals, a phase shifter that coordinates the phase of the input signal based on a control signal, first and second AGC amplifiers that perform gain control so that amplitude becomes constant and a phase comparison mixer that multiplies the output signal of the first AGC amplifier by the output signal of the second AGC amplifier and outputs a phase comparison result signal indicating a phase difference. Moreover, the SD COMB board includes a control circuit that outputs a control signal in accordance with the phase comparison result signal, first and second detection circuits that output first and second detection signals indicating presence or absence of input signals, a third detection circuit that detects an instrument abnormality and an input signal abnormality based on the phase comparison result signal, the first detection signal and second detection signal, and an alarm means that displays the instrument abnormality or the input signal abnormality based on the detection result of the third detection circuit.